A near-infrared radar device may be provided in a vehicle so as to detect a distance from or a relative speed with respect to an object including a preceding vehicle, a pedestrian, and the like using near-infrared radiation. A near-infrared sensor constituting a part of the near-infrared radar device includes a near-infrared transmitting unit and a near-infrared receiving unit. The transmitting unit and the receiving unit are covered with a near-infrared sensor cover through which near-infrared radiation penetrates. In the near-infrared sensor, near-infrared radiation is transmitted from the transmitting unit to outside of the vehicle through the near-infrared sensor cover. Near-infrared radiation reaching and reflected by the object outside the vehicle is received by the receiving unit through the near-infrared sensor cover. The distance or the relative speed is detected via the transmission and reception of near-infrared radiation.
In the near-infrared radar device, when snow is attached to the near-infrared sensor cover, the detection is temporarily stopped since the transmission of near-infrared radiation is prevented. However, the detection is desired to be performed even during snowfall with spread of the near-infrared radar device.
Accordingly, it is considered to dispose a heater wire on the near-infrared sensor cover, so that the snow is melted by heat generated by the energized heater wire (see, for example, JP-A-2005-268015).
However, the near-infrared radiation may be irradiated to the heater wire and reflected when the heater wire is wired to the near-infrared sensor cover as described in JP-A-2005-268015 since the heater wire is formed of metal. The near-infrared radiation penetrating through the near-infrared sensor cover is reduced by an amount of the reflected near-infrared radiation, which may affect a detection function of the near-infrared sensor.